A total of 147 outpatients waiting for a prescription to be filled at a hospital pharmacy were tested on their knowledge about diazepam (Valium). Subjects scored highest on questions about the effects of a small overdose, the drug's interaction with alcohol and hypnotics, and the relative contraindications of pregnancy and breast-feeding. Subjects were least knowledgeable about the drug's generic name, side effects, and interaction with minor stimulants (coffee, tea, cola, and cigarettes). Subjects who had previously used diazepam (N=97) knew significantly more than subjects who had never taken it, but subjects waiting for a diazepam prescription to be filled (N=40) were not more knowledgeable than subjects having another type of prescription filled. In contrast to recent findings that increasing patients' drug knowledge via Patient Package Inserts (PPIs) may also create an overcautious attitude toward the drug, the present study finds that diazepam knowledge gained experientially is accompanied by an attitude shift away from such overcautiousness.